天然气对清洁压裂液的破胶实验

EFFECTS OF NATURAL GAS ON VISCOELASTIC SURFACTANT(VES) FRACTURING FLUIDS

黏弹性表面活性剂(VES)清洁压裂液由于低伤害等特点已广泛应用于压裂与防砂等作业。原油和地层水对VES破胶机理与实验研究已相当充分,但天然气对VES的破胶作用至今无公开的实验数据,影响了清洁压裂液在气井改造中的推广应用。为此设计了一套实验流程,通过流变仪测量VES内充入天然气后的黏度变化,评价了天然气和套管伴生气对3种VES压裂液的影响。实验证明,不同类型的VES被天然气降黏幅度存在较大差别,降黏幅度随天然气的压力升高而提高,随天然气中C2以上成分含量的提高而增高。实验评价的阳离子型和两性离子型的VES可在低压下大幅度被天然气降黏,而阴离子型降黏需要较高压力。二氧化碳对降黏阴离子型的VES有一定影响,而对阳离子型和两性离子型的VES没有影响。被天然气降黏后的VES经过真空脱气后,黏度不能恢复,说明真空条件不能破坏天然气与VES的胶束结构,经天然气破胶的VES重复利用还存在技术困难。

Breaking mechanisms of viscoelastic surfactant(VES) gelled fluids used for fracpacking and conventional hydraulic fracturing relied on reservoir water and /or oil have been researched extensively.Several papers have pointed out that natural gas may break(reduce) the fluids gel viscosity,however,no documents support their points.This paper describes an experimental procedure to evaluate the effects of natural gas on VES fracturing fluids and three types of VES have been tested by natural gas and the associated gas from casing pipes.The test shows that a.for dry methane,the cationic and zwitterions VES may be broken easily,and the anionic just broken slightly in the testing condition;b.breaking efficiency has a good relevance with the pressure;c.a little C2+ hydrocarbons would have great effect on the viscosity of the VES;d.CO2 has great effect on the anionic VES,but no effect on the cationic and zwitterions VES;e.the viscosity of the broken VES can not be recovered by removing the gas in vacuum,which makes it difficult for the reuse of the VES.